Self Assessment 2025-26 — Deadlines, Penalties & Who Needs to File
Everything you need to know about filing your UK Self Assessment tax return for the 2025-26 tax year (6 April 2025 to 5 April 2026).
Key dates for Self Assessment 2025-26
Self Assessment penalties for late filing
| When | Penalty | Details |
|---|---|---|
| 1 day late | £100 | Automatic penalty from 1 February 2027, even if no tax is owed |
| 3 months late | +£10/day | £10 per day for up to 90 days — maximum additional £900 |
| 6 months late | +5% of tax or £300 | Whichever is higher — adds to the penalties above |
| 12 months late | +5% of tax or £300 | A further charge — can be higher if deliberate non-filing |
| Late payment | Interest + 5% | Daily interest from 1 Feb + 5% surcharge at 30 days, 6 months, 12 months |
Note: HMRC interest rate on late payments is currently 7.25% per year (Bank Rate + 2.5%). Penalties and interest compound quickly — file and pay on time.
Do you need to do a Self Assessment? Checklist
You must complete a Self Assessment for 2025-26 if any of the following apply:
Self Assessment for the 2025-26 tax year
The UK Self Assessment system requires individuals to calculate and declare their own tax liability for income that is not taxed at source through PAYE. For the 2025-26 tax year (6 April 2025 to 5 April 2026), the main online filing deadline is 31 January 2027.
First-time Self Assessment filers
If you have never filed before, you must first register with HMRC. You can do this through your Government Gateway account at gov.uk/log-in-file-self-assessment-tax-return. After registering you will receive a Unique Taxpayer Reference (UTR) number — allow up to 10 working days. Always register by 5 October 2026 to file for the 2025-26 year.
Payments on account
If your self-employed or other Self Assessment tax bill exceeds £1,000 (and less than 80% was collected at source), HMRC will require you to make advance payments on account towards the following year. These are split into two equal payments: the first with your January return, the second by 31 July. You can apply to reduce payments on account if you expect your income to be lower.
What records do I need?
Keep records of all income and expenses for at least 5 years after the filing deadline. This includes P60s and P45s, bank statements, sales invoices, rental income records, and any receipts for expenses you are claiming. HMRC can enquire into any return within a year of filing, or longer if they suspect errors or fraud.
Frequently asked questions
Do I need to do a Self Assessment tax return?
You must complete a Self Assessment if in 2025-26 you were self-employed with income over £1,000, had income from renting out property, earned more than £100,000 gross, received untaxed income (savings interest, dividends above allowances, side hustle), had two or more sources of income, or were a company director. HMRC may also send you a notice to file even if you are unsure.
What is the deadline for Self Assessment 2025-26?
For the tax year 6 April 2025 to 5 April 2026: online Self Assessment returns and any tax owed must be filed and paid by 31 January 2027. Paper returns have an earlier deadline of 31 October 2026. If you make payments on account, the second payment is due 31 July 2026 (for 2024-25). You must register for Self Assessment by 5 October 2026 if you have not done so before.
What are the penalties for late Self Assessment?
If you miss the 31 January 2027 deadline: an automatic £100 penalty applies on day 1. After 3 months (30 April 2027), £10 per day for up to 90 days (maximum £900). After 6 months, 5% of the tax due or £300 (whichever is higher). After 12 months, a further 5% or £300. Interest also accrues on unpaid tax from 1 February 2027.
What are payments on account?
If your Self Assessment tax bill is over £1,000, HMRC requires you to make advance payments towards the following year's bill. These are called payments on account — two equal instalments due 31 January (with your return) and 31 July. Each is 50% of the previous year's tax bill. If your income changes significantly you can apply to reduce payments on account.
How do I register for Self Assessment?
Register online at gov.uk/log-in-file-self-assessment-tax-return. If you are self-employed, you also register as a sole trader. You will receive a Unique Taxpayer Reference (UTR) number within 10 working days. For 2025-26, you must register by 5 October 2026. HMRC can charge a penalty if you fail to notify them of a new tax liability on time.